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Abstract. Insoluble atmospheric aerosol, such as mineral dust, hasbeen identified as an important contributor to the cloud droplet numberconcentration and indirect climate effect. However, empirically derivedFrenkel–Halsey–Hill (FHH) water adsorption parameters remain the largestsource of uncertainty in assessing the effect of insoluble aerosol onclimate using the FHH activation theory (FHH-AT). Furthermore, previouslyreported FHH water adsorption parameters for illite and montmorillonitedetermined from water adsorption measurements below 100 % RH do notsatisfactorily agree with values determined from FHH-AT analysis ofexperimental cloud condensation nuclei (CCN) measurements undersupersaturated conditions. The work reported here uses previously reportedexperimental water adsorption measurements for illite and montmorilloniteclays (Hatch et al., 2012, 2014) to show that improvedanalysis methods that account for the surface microstructure are necessaryto obtain better agreement of FHH parameters between water adsorption andexperimental CCN-derived FHH parameters.